We will refer to matrices \(V_k\)  as reduced channel matrices. In particular, usual zero-forcing is obtained if \(B_k = I\) , and \(V_k=H_k\)  are whole channel matrices. Less trivial example is given by eigen zero-forcing (abbreviated as EZF, [1]}), which determines \(B_k\)  by the following procedure. Write SVD decomposition of channel \(H_k = \mathcal {U}_k\mathcal {S}_k\mathcal {V}_k\) . Then \(B_k = I^{\prime } \mathcal {S}_k^{-1} \mathcal {U}_k^{-1}\) , where \(I^{\prime } = \begin{pmatrix} I | 0 \end{pmatrix}\) , so that \(V_k\)  is the upper cut of \(\mathcal {V}_k\) . Precoding itself is calculated as pseudo-inverse of concatenated matrices \(V_k\) , which is one of possible ways to satisfy conditions of RCZF.
